The instant invention relates to an electronic system for regulating vehicle braking and/or vehicle starting. The regulating system monitors the speeds of each of the vehicle wheels and detects deviations in the rotational speeds of the individual wheels from a mean speed.
A system of this general type is known from EP-A-29 35 61.
Electronic regulating systems which regulate braking or starting of a vehicle have been known for some time. Their functions are mainly to decrease to an optimal value brake slippage when the vehicle is braked, or wheel slippage when the vehicle is started. Such regulating systems are commonly known as antilock braking (ABS) systems and drive slip control (ASR) systems, respectively. As a result of the regulation provided by an ABS system, the stopping distance upon braking is reduced to a minimum while the maneuverability of the vehicle is maintained. In the case of an ASR system, spinning of the drive wheels is prevented upon starting and the starting of the vehicle is thus improved. Modern electronic regulating systems often combine both ABS and ASR functions in a single, integrated electronic regulating system.
To be able to provide reliable and optimal regulation, such systems require the most exact possible input data. The most important input data in this case are the rotational speeds of the wheels which are supplied by wheel sensors mounted at the peripheries of the wheels.
It is possible that in some cases the rotational speeds of individual wheels may continuously diverge from the mean value of the speeds of all the wheels or from the mean value of the speeds of the wheels mounted on a reference axle. These divergences can be caused by differences in tire diameters due to wear, due to manufacturing tolerances, or due to the fact that different types of tires are mounted on the front axle and on the rear axle. Such a pairing of dissimilar tire types does indeed occur in practice.
Differences in rotational speeds of the wheels can also be caused by a faulty installation of a pole wheel facing the wheel sensor. For instance, a pole wheel with 80 teeth could have been installed opposite a wheel where a pole wheel having 100 teeth was required. As a result, a wheel that appears to run too slowly would be sensed.
Because of wheels with different tire diameters or outer circumferences, early or belated slippage signals may be produced in a vehicle provided with ABS and/or ASR regulation. As a result, the quality of regulation, for example, the comfort provided by the regulation, is reduced.
Faulty installation of pole wheels on front and rear axles constitutes a safety problem, especially with antilock brake systems which utilize a reference speed derived from several individual wheel speeds. It may then occur that no pressure or insufficient braking power is applied to wheels or axles when individual wheels are sensed as running apparently at insufficient speed.
A method is already known according to which the speeds of all the tires are compared with each other so that individual tires with slightly higher rotational speeds can be detected in order to identify tires with insufficient air pressure (see, e.g., DE-OS 25 18 816). However, this patent document does not suggest an application to an antilock brake system or to starting regulation, and is not suitable for belted tires.
The above-mentioned EP-A-29 35 61, which deals essentially with the detection of turns, also deals with the detection of a smaller diameter in a so-called spare wheel which is mounted in case of failure of a normal wheel. Such spare wheels have an outer circumference that is up to 20% below that of standard wheels. Spare wheel detection is effected by comparing "turn travel signals" of the forward and rear axles.
If these signals are different from each other over a long period of time, the electronic system concludes that such a spare wheel has been mounted. By means of a reduction of the measured rotational speeds that is internal to the electronics, or by switching the logic, the deviations can be compensated for and regulation can be adapted to special situations. However, this known patent document does not give any further details.
It is the object of the instant invention to provide an electronic regulating system for vehicle braking or starting of the type mentioned initially so that when minor continuous speed variations of individual wheels occur, a better regulating quality is achieved.